1. Field of the Invention
This invention relates to a device for adjusting a focal plane shutter driving spring arranged to permit automatic adjustment of the spring.
2. Description of the Prior Art
Heretofore, the driving springs of a focal plane shutter consisting of metal blades have been provided with adjustment devices, which are arranged as shown in FIGS. 1 and 2 of the accompanying drawings. The conventional arrangement shown includes a shutter base plate 1 and a cover plate 2. Between the base plate 1 and the cover plate 2, there are provided leading and trailing shutter curtains each of which consists of a plurality of divided blades linked with a driving lever and an auxiliary lever which is not shown. In FIG. 1, trailing shutter blades 4.sub.1 -4.sub.5 are shown as in a state of covering an aperture. A base plate 5 of a shutter control part is connected to the shutter base plate 1 by posts 6 and 7 and other posts which are not shown. The post 6 has a trailing curtain driving lever 3 and a ratchet wheel 8 rotatably fitted thereon. Between the lever 3 and the wheel 8, there is wound a trailing curtain driving spring 9. One end of the spring 9 is fitted in and retained by a groove provided in the ratchet wheel 8. The other end of the spring is hooked on a pin 3b disposed on the driving lever 3. There are also provided a ratchet pawl 10, a leading shutter curtain driving lever 11, a leading curtain driving spring 12, a ratchet wheel 13 and a ratchet pawl 14 all of which are provided for the leading shutter curtain and are arranged in a manner similar to the parts provided for the trailing curtain.
Referring now to FIG. 2, in the conventional arrangement described above, the ratchet wheel 8 is rotated counterclockwise for strengthening the driving force of the spring. To slacken the spring, the pawl 10 is disengaged from the ratchet teeth and the ratchet wheel 8 is rotated clockwise. Such adjustment work on the spring has been manually carried out in general. However, the adjustment work has been extremely troublesome because during the adjustment and particularly when the spring 9 is to be slackened, the ratchet pawl 10 is removed and then the ratchet wheel 8 must be turned while keeping it under the same condition.
Further, automation of the assembly of cameras and shutters has recently become more advanced. However, since the teeth of the ratchet wheel 8 are very minutely arranged for fine adjustment, it is quite difficult to have the ratchet wheel rotated with teeth engaged. Hence, despite the advanced automation of the assembly work, it has been inevitable that in this adjustment work, recourse has been had to manual operation.